. Annual report . herefore, soon attracted the attention ofobservers; and Hall has figured [1865, ] a number of such germswithout, however, referring them to any definite species. He also recognizedclearly that the growth of the rhabdosome begins with the minute spinelike 520 NEW YORK STATE MUSEUM body which he termed the initial point or radicle, and for whichLapworth later on introduced the term sicula. The details of the structure of the sicula have been elucidated byWiman, who has demonstrated that it consists of two very different parts[see , 2a, 2b]. The initial part is a smooth
. Annual report . herefore, soon attracted the attention ofobservers; and Hall has figured [1865, ] a number of such germswithout, however, referring them to any definite species. He also recognizedclearly that the growth of the rhabdosome begins with the minute spinelike 520 NEW YORK STATE MUSEUM body which he termed the initial point or radicle, and for whichLapworth later on introduced the term sicula. The details of the structure of the sicula have been elucidated byWiman, who has demonstrated that it consists of two very different parts[see , 2a, 2b]. The initial part is a smooth1, thin walled conical body thatdoes not show any transversal growth lines and tapers at one end into ahollow tube, the nema, while the other, wider end is directly continuouswith the apertural part of the sicula, which is the larger and thicker Pig. :3 D i p 1 o gr ap tu s sp. Sicula,showing the characters of the apical(embryonic) and apertural the Baltic sea limestone ofBornholm. x37 (Copy from Wiman). Fig. 2a Fig. 2b Fig-. 2a, 2b. Obverse and reverse views of 1 lieyoung rhabdosome of a diehograptid showingthe sicula, its two parts and the gemmation ofthe first theca. From the Asaphus-limestoneof Oeland. x27 (Copies from Wiman) walled portion; is provided with growth lines and in form approaches atheca. The sicula has for this reason been termed the hrst theca by Holm. The question appears pertinent, whether in the sicula itself (its apicalpart) we have to see a product of sexual reproduction or of some form ofgemmation. This leads to the further inquiry after the organ of rep rodactionof the graptolites. Hall believed he had found such organs in appendages of therhabdosomes of D i p 1 o g r a p t us w h i t f i e 1 d i | 1859, ], whichgive the impression of macerated or ruptured vesicles. But no siculae werefound in connection or inclosed in them ; and a large series of specimens of :In Diplograptus provided with longitudinal anastomosing thickenings. GRAPTOL
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